In manufacturing positive electrodes for cells in which manganese dioxide is used as an active material, a paste-type method may be considered for obtaining a thin positive electrode having high-rate discharge characteristics. In this case, it may be proposed to add to manganese dioxide active material powder, a viscous agent solution also serving as a binder such as polyvinyl alcohol or methyl cellulose, thereby to form paste, which is subsequently applied to or coated on the supporting member, and to heat-treat such paste-applied or paste-coated supporting member at temperatures lower than the decomposition temperature of the viscous agent. This method is inconvenient, particularly in the case of the positive electrodes for nonaqueous cells because positive electrodes used for nonaqueous cells should be activated with substantially all water removed. However, at temperatures around 200.degree. C. combined water may not be removed from the manganese dioxide, although adherent water may be removed. In order to remove the combined water, it is therefore necessary to perform heat-treatment at temperatures higher than 250.degree. C., preferably in the range from 350.degree. C. to 430.degree. C.
Alternatively, it is possible to prepare starting active material of manganese dioxide from which adherent water and combined water have been removed as far as possible by previously heat-treating the manganese dioxide at temperatures in the range from 350.degree. C. to 430.degree. C. In this case, however, when such manganese dioxide is mixed with a conductive agent and a viscous agent during the manufacture, water is again adhered to the manganese dioxide. For removing such re-adhered water, it is required to perform heat-treatment at temperatures higher than 200.degree. C., preferably at a temperature of approximately 300.degree. C. However, when a viscous agent decomposable at a temperature of about 200.degree. to 280.degree. C. such a polyvinyl alcohol or methyl cellulose alone is also used as a binder, it is not possible to perform heat-treatment at temperatures higher than the decomposition temperature of such a viscous agent.
Accordingly, the thus described method of using only a viscous agent serving also as a binder is not acceptable as a method of manufacturing the positive electrodes for nonaqueous cells.
In order to overcome the inconveniences above-mentioned, it may be proposed to use, in addition to a viscous agent used for forming paste, fluoric resin, nylon or the like having a melting point (about 300.degree. C.) higher than the decomposition temperature of the viscous agent. However, it has been found that the performance of a cell manufactured according to this method depends on the atmosphere in which the heat-treatment was carried out. Namely, when a viscous agent and a binder are added to manganese dioxide active material powder and heat-treatment is subsequently performed at a temperature of about 300.degree. C. under vacuum or in an inert atmosphere, the viscous agent is decomposed at a temperature in the vicinity of 200.degree. C. This decomposition is an oxygen consuming reaction, in which the manganese dioxide is reduced, thereby to decrease the amount of effective manganese dioxide, thus resulting in a decrease in the discharge capacity.